Adhesive/Sealing Material for an Electrowetting Device

ABSTRACT

Subject matter disclosed herein relates to improving a contact diameter of an adhesive/sealing material on surfaces of substrates by altering rheological properties of the adhesive/sealing material. An electrowetting display device comprises a first substrate and a second substrate, a first fluid and a second fluid disposed between the first substrate and the second substrate, wherein the first fluid is immiscible with the second fluid. An adhesive/sealing material comprising UV curable epoxy glue is in contact with the second fluid and couples the second substrate to the first substrate. The adhesive/sealing material further comprises silica particles in a range of 1-6% mass fraction of silica that alter rheological properties of the UV curable epoxy glue.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims priority to U.S. patentapplication Ser. No. 15/288,743, which is a divisional of U.S. patentapplication Ser. No. 14/278,831, filed on May 15, 2014, now known asU.S. Pat. No. 9,465,206, issued on Oct. 11, 2016, which claims priorityto U.S. Provisional Patent Application No. 61/935,789, filed on Feb. 4,2014, which is incorporated herein by reference.

BACKGROUND

Many portable electronic devices include displays for displaying varioustypes of images. Examples of such displays include electrowettingdisplays (EWDs), liquid crystal displays (LCDs), electrophoreticdisplays (EPDs), light emitting diode displays (LED displays), etc. InEWD applications, two substrates or support plates are coupled togetherwholly or partially under or in contact with electrowetting fluids usingan adhesive or other sealing material. After positioning a top substrateand filling the substrates with electrowetting fluids, the top substrateneeds to be attached to a bottom substrate. A sealing material such as,for example, ultraviolet (UV) curable epoxy glue, is used for attachingthe top and bottom substrates to one another. The uncured glue isdispensed in a desired pattern on the top substrate before thesubstrates filling process commences, wherein the glue can be dispensedin globular deposits or as a substantially continuous pattern of glue onthe periphery of the top substrate before filling with electrowettingfluids and coupling the two substrates into a EWD device. During fillingand coupling, the uncured glue is predominantly in contact with a secondfluid of the two fluids. When the uncured glue comes into contact or isimmersed in the second fluid, an undesirable fluid-flow phenomenonoccurs that renders the application of the glue cumbersome, for example,when the glue is under the second fluid. This phenomenon can beexplained with respect to FIG. 1, which is a cross-sectional view of aline of uncured glue on a substrate.

When a line of uncured ultraviolet (UV) curable epoxy glue 100 isimmersed in a second fluid 102, which, for example, may be electricallyconductive or polar, and may be water or a salt solution such as asolution of potassium chloride in a mixture of water and ethyl alcohol,the dispensed UV curable epoxy glue 100 may be pushed back, adverselydisplaced or dismounted from the substrate by the force of the secondfluid (represented as Ffluid in FIG. 1). The polarity of the secondfluid 102 matches better with the polarity of a conducting layer ofmaterial such as an indium tin oxide (ITO) layer 104 (e.g., an ITO layer104 on a substrate 106) in comparison to the polarity of the UV curableepoxy glue 100, since both the second fluid 102 and the ITO 104 arehydrophilic while the UV curable epoxy glue 100 is more hydrophobic. Thesecond fluid 102 begins to compete with the UV curable epoxy glue 100 towet the ITO surface 104. Because of this competition the contactdiameter (d) of the UV curable epoxy glue 100 with the ITO surface 104decreases (dair>dfluid), where dair represents the contact diameter ofthe UV curable epoxy glue 100 with the ITO surface 104 in air upon beinginitially dispensed and dfluid represents the contact diameter of the UVcurable epoxy glue 100 with the ITO surface 104 in the second fluid 102.A decrease in contact diameter is a problem because it leads to adecrease in adhesion of the top and bottom substrates.

Accordingly, the behavior of the UV curable epoxy glue 100 under thefluid 102 results in drawbacks in manufacturing of EWD display devices.For example, extra time and space may be needed in the manufacturingline.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description is described with reference to non-limiting andnon-exhaustive embodiments illustrated in the accompanying figures. Thesame reference numerals in different figures refer to similar oridentical items.

FIG. 1 is a schematic illustration of the effects of gravity and fluidon contact diameter of an adhesive/sealing material on a surface of asubstrate.

FIG. 2A is a schematic view of an example of an electrowetting displaydevice, according to various embodiments.

FIG. 2B is a cross-section of a portion of the electrowetting displaydevice of FIG. 2A, according to some embodiments.

FIGS. 3A-3C are schematic views illustrating simplified example stagesof assembly of a portion of the electrowetting display device of FIGS.2A and 2B.

FIGS. 4A-4C are graphs illustrating yield stress and viscosity inNewtonian fluids, non-Newtonian fluids and real systems, respectively.

FIG. 5 is a schematic illustration of the effects of gravity and fluidon contact diameter of an adhesive/sealing material on a surface of asubstrate, where rheological properties of the adhesive/sealing materialhave been altered.

FIG. 6 is a flowchart illustrating an example of a process of couplingtwo substrates in manufacturing an electrowetting device.

FIG. 7 illustrates select components of an example image displayapparatus that may include an electrowetting display, according tovarious embodiments.

DETAILED DESCRIPTION

The present disclosure provides substances and techniques that providefor improving a contact diameter and influencing the wettability of anadhesive/sealing material on surfaces of substrates in electrowettingdevices by altering rheological properties of the adhesive/sealingmaterial.

In general, image display apparatuses, such as, for example, variouselectronic devices, including, but not limited to, portable computingdevices, tablet computers, laptop computers, notebook computers, mobilephones, personal digital assistants (PDAs), and portable media devices(e.g., e-book devices, DVD players, etc.), display images on a display.Examples of such displays include, but are not limited to, LCDs, EWDsand EPDs.

More particularly, a display device, such as an electrowetting displaydevice, for example, can be a thin film transistor electrowettingdisplay (TFT-EWD) that generally includes an array of transmissive,reflective and/or transflective pixels configured to be operated by anactive matrix addressing scheme. For example, rows and columns of pixelsare operated by controlling voltage levels on a plurality of sourcelines and gate lines. In this fashion, the display device can produce animage by selecting particular pixels to transmit, reflect or blocklight. Pixels are addressed (e.g., selected) via rows and columns of thesource lines and gate lines that are connected to transistors (e.g.,used as switches) included in each pixel. Transistors take up arelatively small fraction of the area of each pixel. For example, thetransistor can be located underneath the reflector in reflectivedisplays.

Electrically, the pixel is a small capacitor with a layer of insulatingoptical material (e.g., liquid crystal material or electrowettingmaterial) sandwiched between two substrates, wherein each substrategenerally includes a transparent conductive indium tin oxide (ITO)layer. A one-way current-passing characteristic of the transistor of thepixel prevents charge that is being applied to the pixel from drainingbetween refresh cycles of the display's image.

An electrowetting display employs an applied voltage to change thesurface tension of a liquid in relation to a surface. For instance, byapplying a voltage to a hydrophobic surface via a pixel electrode inconjunction with a common electrode, the wetting properties of thesurface can be modified so that the second fluid has a greater affinityfor the surface. Hydrophobic generally refers to repelling polar fluidswhile hydrophilic generally refers to having an affinity for polarfluids. As one example of an electrowetting display, the modification ofthe surface energy by applying a voltage causes the electrolyte,considered to be the second fluid, in an electrowetting liquid inindividual pixels of the display to adhere to the modified surface andthus, replace a colored electrowetting oil layer in individual pixels ofthe display. The electrowetting oil layer is generally made up of an oilthat is electrically non-conductive and may for instance be an alkanelike hexadecane or silicone oil. Thus, the electrowetting fluids in theindividual pixels of the display responding to the change in surfacetension act as an optical switch. When the voltage is absent, thecolored electrowetting oil forms a continuous film within a pixel, andthe color may thus be visible to a user of the display. On the otherhand, when the voltage is applied to the pixel, the coloredelectrowetting oil is displaced and the pixel becomes transparent. Whenmultiple pixels of the display are independently activated, the displaycan present a color or grayscale image. The pixels may form the basisfor a transmissive, reflective, or transmissive/reflective(transreflective) display. Further, the pixels may be responsive to highswitching speeds (e.g., on the order of several milliseconds), whileemploying small pixel dimensions. Accordingly, the electrowettingdisplays herein may be suitable for applications such as displayingvideo and/or static content. In addition, the low power consumption ofelectrowetting displays in general makes the technology suitable fordisplaying content on portable display devices that rely on batterypower.

To provide a suitable seal to attach the two substrates, an idealadhesive for gluing and sealing under fluids, such as the second fluid,would be an adhesive that does not change geometry if it is dispensed inair or immersed in a fluid. In an embodiment, the rheology orrheological properties of the adhesive or sealing material are changed.This can be achieved by, for example, increasing the viscosity of theadhesive. Moreover, high viscosity adhesive may have additionaldrawbacks, for example, the adhesive may become very hard to dispensefrom its dispenser or dispensing apparatus during manufacturing.

Moreover, to provide a suitable seal to attach the two substrates, thesurface tension, for example, of the second fluid may have a surfacetension surface tension greater than 35, 40, 45 or 50 mN m <1>. Thesurface tension of the adhesive or seal may be greater than 40, 45, or50 mN m <1>.

Referring to FIG. 2A, an example of an electrowetting display device 200is schematically illustrated that includes a timing controller 202, adata driver 204, a scan driver 206, a voltage generator 208, and anelectrowetting display panel 210. The electrowetting display panel 210is driven by the timing controller 202, the data driver 204, the scandriver 206, and the voltage generator 208.

As an example of general operation of the electrowetting display device200, responsive to a first data signal DG1 and a first control signal C1from an external source, e.g., a graphic controller (not illustrated),the timing controller 202 applies a second data signal DG2 and a secondcontrol signal C2 to the data driver 204; a third control signal C3 tothe scan driver 206; and a fourth control signal C4 to the voltagegenerator 208.

The data driver 204 converts the second data signal DG2 to voltages,i.e., data signals, and applies the data signals D1, . . . , Dp−1, Dp,Dp+1, . . . , Dm to the electrowetting display panel 210. The scandriver 206 sequentially applies scan signals S 1, . . . , Sq−1, Sq, . .. , Sn to the electrowetting display panel 210 in response to the thirdcontrol signal C3.

The voltage generator 208 applies a common voltage Vcom to theelectrowetting display panel 210 in response to the fourth controlsignal C4. Although not illustrated in FIG. 2A, the voltage generator208 generates various voltages required by the timing controller 202,the data driver 204, and the scan driver 206.

The electrowetting display panel 210 includes m data lines DL, i.e.,source lines, to transmit the data voltages and n gate lines SL, i.e.,scan lines, to transmit a gate-on signal.

Pixel areas 212 are positioned adjacent to crossing points of the datalines DL and the gate lines SL crossing the data lines DL. Each pixelarea 212 is made up of a hydrophobic surface that includes a thin filmtransistor 214 and a pixel electrode 216 under the hydrophobic surface.A partition wall 218 defines the pixel area 212. Pixel areas 212 canrepresent pixels within the electrowetting display device 200 orsub-pixels within the electrowetting display device 200, depending uponthe application for the electrowetting display device 200.

FIG. 2B is a cross-section of a portion of the electrowetting device 200illustrating several electrowetting elements 220 that generallycorrespond to pixel areas 212, according to some embodiments. Anelectrode layer 222 that includes the pixel electrodes 216 (notillustrated in FIG. 2B) is formed on a bottom support plate 224. In someimplementations, a dielectric barrier layer (not illustrated) may atleast partially separate the electrode layer 222 from a hydrophobiclayer 226 also formed on the bottom support plate 224 over the electrodelayer 222. Such separation can, among other things, prevent electrolysisoccurring through the hydrophobic layer 226. In some implementations,the hydrophobic layer 226 can comprise a fluoropolymer, such as AF1600,produced by DuPont, based in Wilmington, Del. The pixel walls 218 form apatterned electrowetting element grid on the hydrophobic layer 226, ascan be seen in FIG. 2A. The pixel walls 218 may comprise a photoresistmaterial, such as epoxy-based negative photoresist SU-8. The patternedelectrowetting element grid comprises rows and columns that form anelectrowetting element array (e.g., electrowetting display panel 210) offield electrowetting elements and border electrowetting elements. Forexample, an electrowetting element can have a width and length in arange of about 50 to 500 microns. A first fluid 228, which can have athickness in a range of about 1 to 10 microns, for example, overlies thehydrophobic layer 226. The first fluid 228 is generally anelectrowetting oil and is partitioned by the pixel walls 218 of thepatterned electrowetting element grid. An outer rim 230 can comprise thesame material as the pixel walls 218. A second fluid 232, such as afluid that includes an electrolyte, overlies the electrowetting oil 228and the pixel walls 218 of the patterned electrowetting element grid.

A top support plate 234 covers the second fluid 232 and edge seals 236retain the second fluid 232 over the electrowetting element array. Thebottom support plate 224 and the top support plate 234 may be separateparts of individual electrowetting elements or the bottom support plate224 and the top support plate 234 may be shared by a plurality ofelectrowetting elements. The bottom support plate 224 and the topsupport plate 234 may be made of glass or polymer and may be rigid orflexible, for example.

A voltage V applied across the second fluid 232 and the dielectricbarrier layer stack (e.g., comprising the electrode layer 222 and thehydrophobic layer 226) of individual electrowetting elements can controltransmittance or reflectance of the individual electrowetting elements.

The electrowetting display device 200 has a viewing side 238 on which animage or display formed by the electrowetting display device 200 can beviewed, and a rear side 240. The top support plate 234 faces viewingside 238 and the bottom support plate 224 faces the rear side 240. Thetop support plate 234 is coupled to the bottom support plate 224 with anadhesive or sealing material (not illustrated). In an alternativeembodiment, the electrowetting display device 200 may be viewed from therear side 240. The electrowetting display device 200 may be areflective, transmissive or transreflective type. The electrowettingdisplay device 200 may be a segmented display type in which the image isbuilt up of segments. The segments can be switched simultaneously orseparately. Each segment includes one electrowetting element 220 or anumber of electrowetting elements 220 that may be neighboring or distantfrom one another. The electrowetting elements 220 included in onesegment are switched simultaneously, for example. The electrowettingdisplay device 200 may also be an active matrix driven display type or apassive matrix driven display, just to name a few examples.

The second fluid 232 is immiscible with the first fluid 228. Generally,immiscible refers to the inability of the second fluid 232 to mix orblend with the first fluid 228. The second fluid 232 generally includesan electrolyte and is electrically conductive or polar. The second fluid232 may be water or a salt solution such as a solution of potassiumchloride in a mixture of water and ethyl alcohol, for example. Thesecond fluid may comprise at least one component selected from the groupconsisting of: ethylene glycol; diethyleneglycol; polyethylene glycol;propylene glycol; dioxalane; glyoxal; citric acid; oxalic acid; oxamicacid; and formic acid; and includes a second component which isdifferent from the first component and is selected from the groupconsisting of: erythritol; ethylene glycol; ethylene carbonate;propylene carbonate; glycerol; and butanetriol.

The second fluid 232 is preferably transparent, but may be colored,white, absorbing or reflecting. The first fluid 228, generally referredto as electrowetting oil, is electrically non-conductive and may forinstance be an alkane like hexadecane or silicone oil. The hydrophobiclayer 226 is arranged on the bottom support plate 224 to create anelectrowetting surface area. The hydrophobic character causes the firstfluid 228 to adhere preferentially to the bottom support plate 224 sincethe first fluid 228 has a higher wettability with respect to the surfaceof the hydrophobic layer 226 than it has with respect to the secondfluid 232. Wettability relates to the relative affinity of a fluid forthe surface of a solid. Wettability increases with increasing affinity,and it can be measured by the contact angle formed between the fluid andthe solid and measured internal to the fluid of interest. For example,such a contact angle can increase from relative non-wettability of morethan 90° to complete wettability at 0°, in which case the fluid tends toform a film on the surface of the solid.

The electrode layer 222 is separated from the first fluid 228 and thesecond fluid 232 by an insulator, which may be the hydrophobic layer226. The electrode layer 222 (and thereby the electrodes 216) issupplied with voltage signals V by a first signal line 242 as will befurther described herein. A second signal line 244 is electricallyconnected to a top electrode (not illustrated) that is in contact withthe conductive second fluid 232. This top electrode may be common tomore than one electrowetting element 220 since the electrowettingelements 220 are fluidly interconnected by and share the second fluid232 uninterrupted by the pixel walls 218. The electrowetting elements220 are controlled by the voltage V applied between the first and secondsignal lines 242 and 244.

The first fluid 228 absorbs at least a part of the optical spectrum. Thefirst fluid 228 may be transmissive for a part of the optical spectrum,forming a color filter. For this purpose, the first fluid 228 may becolored by addition of pigment particles or dye, for example.Alternatively, the first fluid 228 may be black (e.g., absorbingsubstantially all parts of the optical spectrum) or reflecting. Thehydrophobic layer 226 may be transparent or reflective. A reflectivelayer may reflect the entire visible spectrum, making the layer appearwhite, or part of it, making it have a color.

When the voltage V applied between the signal lines 242 and 226 is setat a non-zero active signal level, the electrowetting element 220 willenter into an active state. Electrostatic forces will move the secondfluid 232 toward the electrode layer 222, thereby repelling the firstfluid 228 from the area of the hydrophobic layer 226 to the pixel walls218 surrounding the area of the hydrophobic layer 226, to a drop-likeform. This action uncovers the first fluid 228 from the surface of thehydrophobic layer 226 of the electrowetting element 220. When thevoltage across the electrowetting element 220 is returned to anin-active signal level of zero or a value near to zero, theelectrowetting element 220 will return to an inactive state, where thefirst fluid 228 flows back to cover the hydrophobic layer 226. In thisway, the first fluid 228 forms an electrically controllable opticalswitch in each electrowetting element 220.

Generally, the thin film transistor 214 includes a gate electrode (notillustrated) that is electrically connected to a corresponding scan lineof the scan lines SL, a source electrode (not illustrated) iselectrically connected to a corresponding data line (e.g., first signalline 242 of FIG. 2B) of the data lines DL, and a drain electrode (notillustrated) is electrically connected to the pixel electrode 216. Thus,the pixel areas 212 are operated based upon the scan lines SL and thedata lines DL of FIG. 2A.

For briefly describing an example of a manufacturing process of theelectrowetting elements of electrowetting display device 200, referenceis made to FIGS. 3A-3C. For clarity, FIGS. 3A-3C do not include many ofthe elements previously described with respect to FIGS. 2A-2B.

FIG. 3A schematically illustrates a top view of a first substrate 300(e.g., bottom support plate 224). The first substrate 300 includes fourfirst surface areas 302 that are less wettable to the second fluid 232(not illustrated in FIG. 3A) and a second surface area 304 that is morewettable to the second fluid 232. More or fewer first surface areas 302may be included. The second surface area 304 encloses the first surfaceareas 302. The four first surface areas 302 correspond to four pictureelements (e.g., pixel areas 212) of the electrowetting display device200 and are arranged within a display region 306 (e.g., display panel210). When the first fluid 228 is an electrowetting oil and the secondfluid 232 is water, for example, the first surface areas 302 arehydrophobic and the second surface area 304 is hydrophilic.

The wettability properties of the surface areas may be obtained by asuitable choice of substrate material, treatment of the substratesurface or application of a layer on the substrate surface. For claritysake, the figures illustrate the surface areas as a layer. When thesubstrate material provides the properties of the second surface area304, the second surface area extends to the edge of the first substrate300 in FIG. 3A.

As previously noted, the first surface areas 302 may be formed, forexample, by an amorphous fluoropolymer layer such as AF1600 or anotherlow surface energy polymer. The hydrophobic character causes the firstfluid 228 to adhere preferentially to the first surface areas 302 sincethe hydrophobic layer (e.g., hydrophobic layer 226) has a higherwettability with respect to the first fluid 228 than it has with respectto the second fluid 232. The second surface areas 304 may be formed by aphotoresist layer, for example SU8. Where it is stated herein thatadhesive or sealing material is attached to, or a fluid is applied tothe first substrate 300 or a surface or surface area of the firstsubstrate 300, the first substrate 300 is regarded as including anysolid layers arranged on the first substrate 300 (e.g., bottom supportplate 224) as previously discussed herein, such as, for example, thelayers controlling the wettability properties.

FIG. 3B schematically illustrates a top view of a second substrate 308(e.g., top support plate 234). An adhesive/sealing material 310 (e.g.,edge seals 236) is in contact with the second substrate 308 in apre-determined pattern, in this example embodiment a square shapeenclosing the display region 306. The adhesive/sealing material 310 isgenerally an adhesive such as, for example, ultraviolet (UV) curableepoxy glue, and may be dispensed using an injector (not illustrated),such as a syringe or other device having an appropriately dimensionedorifice, that is configured to follow the pre-determined pattern. Thus,the adhesive/sealing material 310 being in contact with the secondsubstrate 308 means that the adhesive/sealing material 310 is in contactwith and may at least partially be adhered to the second substrate 308.To avoid a non-uniform thickness of adhesive/sealing material 310 in thepattern due to the start of the injection of the adhesive/sealingmaterial 310, the injection is preferably started outside the displayregion 306 and then continues towards the pre-determined pattern.Alternatively, the adhesive/sealing material 310 may have the form of aseal frame (not illustrated) that is defined on the first substrate 300.Where it is stated herein that adhesive or sealing material is attachedto, or a fluid is applied to the second substrate 308 or a surface orsurface area of the second substrate 308, the second substrate 308 isregarded as including any solid layers arranged on the second substrate308 (e.g., top support plate 234) as previously discussed herein, suchas, for example, an ITO layer.

FIG. 3C schematically illustrates a cross-section of the first andsecond substrates 300 and 308 before assembly of the two substrates 300,308. The cross-section is along the line A-A in FIG. 3A. FIG. 3Cillustrates the strip of adhesive/sealing material 310 also incross-section. The first substrate 300 has been provided with the firstfluid 228 adjoining only the first surface areas 302. A method ofapplying the first fluid 228 on the first substrate 300 is to submergethe first substrate 302 in a bath of the second fluid 232, e.g. water.The first fluid 228, e.g., electrowetting oil, is dispensed on thesurface of the first substrate 302 by a dispenser (not illustrated)having an elongated opening close to the surface of the first substrate300 and submerged in the second fluid 232. The dispenser is moved overthe surface of the first substrate 300 in a direction perpendicular tothe long direction of the elongated opening. The first fluid isdispensed over the length of the dispenser as a thin film of first fluid228. Since the surface of the first substrate 300 comprises firstsurface areas 302 that are more wettable with respect to the first fluid228 than to the second fluid 232 and second surface areas 304 that aremore wettable to the second fluid 232, the first fluid 228 willpreferentially adjoin the first surface areas 302 and will not cover thesecond surface areas 304.

When the above method of applying the first fluid 228 is used, the stepof joining the two substrates 300, 308 with the adhesive/sealingmaterial 310 is generally carried out in the bath of the second fluid232. The second substrate 308 is put into the bath, where care is takenthat no air is trapped under the second substrate 308. The twosubstrates 302, 308 are aligned and pressed together such that the twosubstrates 300, 308 obtain a desired distance from one another. Theadhesive/sealing material 310 defines a sealing member between the twosubstrates 300, 308. Since the adhesive/sealing material 310 isgenerally an adhesive, the adhesive/sealing material 310 also generallyattaches the first substrate 300 and the second substrate 308 together.The adhesive/sealing material 310 closes off a cavity 312 between thetwo substrates 300, 308. The cavity 312 comprises the first fluid 228adjoining the first surface areas 302 and the second fluid 232 trappedin the cavity 312. FIGS. 3A-3C are schematic and may exaggerate somedimensions for the sake of clarity.

Another method of applying the two fluids 228, 232 on the firstsubstrate 300 and subsequently sealing the fluids 228, 232 within thecavity 312 using the second substrate 308 is described as a slit fillingmethod, which is briefly described below and is published as WO 2012126851, the contents of which are incorporated herein by reference.

The slit filling method is a method of providing a layer of the firstfluid 228 on the first surfaces 302 of the first substrate 300 using anelongate applicator (not illustrated), with an elongate gap being formedbetween the applicator and the surfaces 302. The gap is filled with anelongate globule of the first fluid 228 and an amount of the secondfluid 232 is arranged in contact with the applicator and with theglobule of the first fluid 228. As previously noted, the first fluid 228and the second fluid 232 are immiscible. Also, as previously noted, thefirst areas 302 have a higher wettability for the first fluid 228 thanfor the second fluid 232. The slit filling method further includesapplying a relative motion between the applicator and the first surfaces302 of the first substrate 300. The amount of the second fluid 232 isarranged only on a trailing side of the applicator. The first substrate300 does need not be submersed in a bath filled with the second fluid232 as previously described. Instead, application of a relatively smallamount of the second fluid 232 between the applicator and the firstsubstrate 300 suffices. Other surfaces of the first substrate 300 can bekept free from the second fluid 232, thereby reducing the requirementsof cleaning these surfaces after application of the slit filling method.The slit filling method also obviates the need for large volumes of thesecond fluid 232. The applicator may move with respect to the surface ofthe first substrate 300. The surface of the first substrate 300 may alsobe moved with respect to the applicator. The applicator distributes thefirst fluid 228 over the surface of the first substrate 300 and therebyacts as a spreader. Since the amount of the second fluid 232 is only atthe trailing side of the applicator, the surface of the first substrate300 in front of the applicator is not covered with the second fluid 232.The surface of the first substrate 300 in front of the applicator ispreferably adjoined by a gas, such as air. When the applicator passesover the surface of the first substrate 300, a layer of the first fluid228 is deposited on the first areas 302 and a layer of the second fluid232 is deposited on the layer of first fluid 228. The second fluid 232will not displace the first fluid 228 from the first surfaces 302because of the higher wettability of the first surfaces 302 for thefirst fluid 228. The substrates 300, 308 are subsequently attached toone another and sealed via the adhesive/sealing material 310 to containthe fluids 228, 232, or the substrates 300, 308 may be attached to oneanother and sealed via the adhesive/sealing material 310 as thesubstrate 300 is being filled.

The previously described two methods for applying the two fluids 228,232 on the first substrate 300 and subsequently sealing the fluids 228,232 within the cavity 312 using the second substrate 308 are merelyexamples. Other methods and steps are also possible. For example, theadhesive/sealing material 310 may be applied to the first substrate 300or to both substrates 300, 308, in various methods.

In accordance with various embodiments, the rheology or rheologicalproperties of the adhesive/sealing material 310 (generally in the formof sealing material, adhesive, glue, etc.) are changed. This can beachieved by, for example, increasing the viscosity of theadhesive/sealing material 310. Rheology generally relates to the flowand deformation of materials under applied forces. Generally, theadhesive/sealing material 310 may exhibit complex rheologicalproperties, whose viscosity and viscoelasticity can vary depending uponthe external conditions applied, such as stress, strain, timescale andtemperature.

To alter the rheology of the adhesive/sealing material 310 such that theadhesive/sealing material's geometry is not altered adversely, i.e.minimally deformed, after dispensing or immersing in a fluid, such asthe second fluid 232, a Yield Stress is introduced in theadhesive/sealing material 310. The introduction of a Yield Stress intothe adhesive/sealing material 310 helps ensure that the adhesive/sealingmaterial 310 does not move or displace itself if a force of a liquid isapplied to the adhesive/sealing material 310 that is lower than theYield Stress. Generally, the adhesive/sealing material 310 will notgeometrically change if:

Yield stress>F_(gravity) and Yield Stress>F_(fluid)  (1)

where F_(gravity) represents the force due to gravity and F_(fluid)represents the force due to the second fluid 232 on the adhesive/sealingmaterial 310.

To dispense the adhesive/sealing material 310 with a Yield Stress, theapplied dispense force generally needs to be higher than the YieldStress (Dispense Force>Yield Stress). At a dispense force higher thanthe Yield Stress, the adhesive/sealing material 310 will move while theviscosity is still relative low, which makes the adhesive/sealingmaterial 310 easier to dispense from its dispenser than other highviscosity glues.

In one example, the adhesive/sealing material 310 comprises a UV curableglue that is specified by a viscosity (η) of 120 Pa*s at 25° C. As noshear rate is given at which this viscosity is reached, it impliesNewtonian behavior: viscosity in Newtonian systems is described as thequotient of Shear Tension (τ) and Shear rate (D); for Newtonian fluidsthis quotient is constant at all shear rates. FIGS. 4A and 4B illustrateyield stress and viscosity Newtonian fluids and non-Newtonian fluids,respectively. FIGS. 4A and 4B are theoretical curves. FIG. 4Cillustrates yield stress and viscosity in real systems. By choosing amaterial for adhesive/sealing material 310 that has a Yield Stress it ispossible to have a viscosity that is also 120 Pa*s at 25° C., but thatdoesn't settle after it is dispensed (Shear rate=0). Viscosity of theadhesive/sealing material 310 aids in overcoming the hydrophilicpreference of the electrolyte, i.e. the second fluid 232, to wet thesurface and achieve good contact of the adhesive/sealing material 310with the surface.

In accordance with various embodiments, in order to increase the YieldStress of the adhesive/sealing material 310, silica particles are addedto UV curable epoxy glue that comprises, for example, a two-part epoxyto introduce the Yield Stress. Silica particles can also be incorporatedin UV curable epoxy glue that comprises a one-part epoxy in order tointroduce a Yield Stress in the adhesive/sealing material 310.

Generally, any glue or sealing material may be used in which silicaparticles may be incorporated. It has been shown that at least 1% massfraction of silica particles are generally required in the glue in orderto produce the desired effect of providing a durable and effective sealto provide a mechanically stable electrowetting device, along with longterm display device integrity. Hydrophobic silica particles may be moreadvantageous because they have a very advantageous effect in hydrophobicglue. Silica is generally hydrophilic. Hydrophobic silica is silica thathas hydrophobic groups chemically bonded to the surface. Hydrophobicsilica can be made both from fumed and precipitated silica. Thehydrophobic groups are normally alkyl or polydimethylsiloxane chains.Examples of hydrophobic silica particles include Aerosil® R202 andAerosil® R805. However, hydrophilic particles also have an advantageouseffect in a hydrophilic glue. An example of hydrophilic silica includesAerosil® 300. In the examples herein, the silica consists of smallsilica particles, where the primary particle size is in a range of about7-40 nanometers (nm).

It has been found that with glues from companies such as, for example,Sekisui and Nagase, a range of 1 to 6% mass fraction of silica added tothe glue provides a sufficient Yield Stress to resist the force of thesecond fluid 232 (e.g., F_(fluid)) while still allowing for viscosity ofthe glue to be low enough to allow for dispensing of the glue.

Thus, as can be seen in FIG. 5, the net contact area d_(air) of glue ona surface 312 (e.g., an ITO layer) of the second substrate 308 in airwill generally be substantially maintained such that the net contactarea d_(fluid) on the surface 312 of the second substrate 308 once thesecond fluid 232 is introduced (i.e. once the substrate with theadhesive/sealing material 310 is in contact with or completely immersedin the second fluid 232) is substantially equal to the net contact aread_(air). Thus, the glue has minimally deformed due to the presence ofthe second fluid 232. Advantageously d_(fluid) is such that theinterface between 310 and surface 312 is substantially perpendicular.This leads to improved adhesion of the glue with the increased YieldStress from the silica introduced particles (e.g. adhesive/sealingmaterial 310) on the surface 312 of the second substrate 308, as well asimproved adhesion on a surface (e.g., hydrophobic layer 226) of thefirst substrate 300 when the two substrates 300, 308 are coupled to oneanother.

As much as 6-10% mass fraction of silica added to the glue provides agood Yield Stress to resist the force of the second fluid 232 (e.g.,F_(fluid) of equation (1)) but may increase the viscosity of the gluesuch that it is more difficult to allow for dispensing of the glue.

In general, the particles are capable of forming a three-dimensionalnetwork when the bulk material (i.e., the glue or sealing material) isin rest. If the shear stress (higher than the Yield Stress) is appliedto the bulk material, the three-dimensional network is broken and thebulk material starts flowing. Generally, the ability for silica to builda network strongly depends on the polarity of the silica and thepolarity of the bulk material into which the silica particles aredispersed.

Other particles that may be incorporated in the adhesive/sealingmaterial 310 are clay particles, for example, which have a similareffect as the silica particles. Generally, ceramic particles alsofulfill the same effect and thus may be suitable particles forincorporation into glue for increasing Yield Stress within theadhesive/sealing material 310. In these examples, the particles alsoconsist of small particles, where the primary particle size of the clayparticles and the primary size of the ceramic particles is in a range ofabout 7-40 nm. Additionally, in these examples, a range of 1 to 6% massfraction of clay particles or ceramic particles added to the glueprovides a sufficient Yield Stress to resist the force of the secondfluid 232 (e.g., F_(fluid)) while still allowing for viscosity of theglue to be low enough to allow for dispensing of the glue. In variousembodiments, a combination of silica particles, clay particles and/orceramic particles may be used, where a range of 1 to 6% total massfraction of the combination of silica particles, clay particles and/orceramic particles is added to the glue.

Generally, epoxies, acrylates, silicones and hot-melt are types of gluesor sealing materials that may be used. Incorporated with each of theseglues can be the following particles: bentonite, iron-oxide, nano-carbontubes or micro-sized particles, Microsized and Nanosized CalciumCarbonate, and Salts of aluminium and calcium such as stearates,octoates and naphthenates.

Accordingly, electrowetting devices, e.g., electrowetting display device200, can be made in accordance with methods described herein usingadhesives, glues, sealing materials, etc. that have an increased YieldStress due to the inclusion of particles in the adhesives, glues,sealing materials, etc. This allows for better adhesion of theadhesives, glues, sealing materials, etc. on the substrates, when thefirst or second substrate is processed in the presence of a fluid suchas the second fluid, thereby leading to improved attachment of andsealing between the substrates. Resistance of the sealingmaterial/adhesive to flow of the fluid results in less inclusions in thesealing material/adhesive and thus a more homogeneous barrier, which ismore robust to leakage paths for fluids through the barrier.

While embodiments of the present disclosure have been described withrespect to electrowetting displays, other types of displays can benefitfrom the present disclosure. For example, LCDs, electrophoreticdisplays, cholesteric LCDs, and other display technologies that utilizefluids can benefit from the present disclosure and thus, the presentdisclosure is not limited to electrowetting displays.

Additionally, while embodiments of the present disclosure have beendescribed with respect to coupling and/or sealing two substrates, morethan two substrates may be coupled and/or sealed in accordance withvarious embodiments. For example, more than two substrates may berequired in sealing a multi-layered electrowetting device. Threesubstrates may be coupled together, wherein the top two substrates mayrequire an adhesive/sealing material as described herein so as to couplethe three substrates.

FIG. 6 is a flowchart illustrating a process 600 of coupling twosubstrates during manufacturing of an electrowetting device, for examplean electrowetting device as described in FIGS. 2A, 2B, 3A, 3B and 3C. At602, a first substrate is provided. At 604, a second substrate isprovided. At 606, an adhesive/sealing material is applied on a portionof the first substrate or a portion of the second substrate. At 608, thefirst substrate is coupled to the second substrate via theadhesive/sealing material such that the adhesive/sealing material is incontact with an electrowetting fluid of two fluids disposed between thetwo substrates, wherein the adhesive/sealing material includes particlesthat alter rheological properties of the adhesive/sealing material.

FIG. 7 illustrates select example components of an example image displayapparatus 700 that may be used with the electrowetting display device200 according to some implementations. Other types of displays may alsobe used with the example image display apparatus 700. Such types ofdisplays include, but are not limited to, LCDs, cholesteric displays,electrophoretic displays, electrofluidic pixel displays, photonic inkdisplays, and the like.

The image display apparatus 700 may be implemented as any of a number ofdifferent types of electronic devices. Some examples of the imagedisplay apparatus 700 may include digital media devices and eBookreaders 700-1; tablet computing devices 700-2; smart phones, mobiledevices and portable gaming systems 700-3; laptop and netbook computingdevices 700-4; wearable computing devices 700-5; augmented realitydevices, helmets, goggles or glasses 700-6; and any other device capableof connecting with the electrowetting display device 200 and including aprocessor and memory for controlling the display according to thetechniques described herein.

In a very basic configuration, the image display apparatus 700 includes,or accesses, components such as at least one control logic circuit,central processing unit, or processor 702, and one or morecomputer-readable media 704. Each processor 702 may itself comprise oneor more processors or processing cores. For example, the processor 702can be implemented as one or more microprocessors, microcomputers,microcontrollers, digital signal processors, central processing units,state machines, logic circuitries, and/or any devices that manipulatesignals based on operational instructions. In some cases, the processor702 may be one or more hardware processors and/or logic circuits of anysuitable type specifically programmed or configured to execute thealgorithms and processes described herein. The processor 702 can beconfigured to fetch and execute computer-readable instructions stored inthe computer-readable media 704 or other computer-readable media. Theprocessor 702 can perform one or more of the functions attributed to thetiming controller 202, the data driver 204, and/or the scan driver 206of the electrowetting display device 200. The processor 702 can alsoperform one or more functions attributed to a graphic controller (notillustrated) for the electrowetting display device.

Depending on the configuration of the image display apparatus 700, thecomputer-readable media 704 may be an example of tangible non-transitorycomputer storage media and may include volatile and nonvolatile memoryand/or removable and non-removable media implemented in any type oftechnology for storage of information such as computer-readableinstructions, data structures, program modules or other data. Thecomputer-readable media 704 may include, but is not limited to, RAM,ROM, EEPROM, flash memory or other computer-readable media technology,CD-ROM, digital versatile disks (DVD) or other optical storage, magneticcassettes, magnetic tape, solid-state storage and/or magnetic diskstorage. Further, in some cases, the image display apparatus 700 mayaccess external storage, such as RAID storage systems, storage arrays,network attached storage, storage area networks, cloud storage, or anyother medium that can be used to store information and that can beaccessed by the processor 702 directly or through another computingdevice or network. Accordingly, the computer-readable media 704 may becomputer storage media able to store instructions, modules or componentsthat may be executed by the processor 702.

The computer-readable media 704 may be used to store and maintain anynumber of functional components that are executable by the processor702. In some implementations, these functional components compriseinstructions or programs that are executable by the processor 702 andthat, when executed, implement operational logic for performing theactions attributed above to the image display apparatus 700. Functionalcomponents of the image display apparatus 700 stored in thecomputer-readable media 704 may include the operating system and userinterface module 706 for controlling and managing various functions ofthe image display apparatus 700, and for generating one or more userinterfaces on the electrowetting display device 200 of the image displayapparatus 700.

In addition, the computer-readable media 704 may also store data, datastructures and the like, that are used by the functional components. Forexample, data stored by the computer-readable media 704 may include userinformation and, optionally, one or more content items 708. Depending onthe type of the image display apparatus 700, the computer-readable media704 may also optionally include other functional components and data,such as other modules and data 710, which may include programs, driversand so forth, and the data used by the functional components. Further,the image display apparatus 700 may include many other logical,programmatic and physical components, of which those described aremerely examples that are related to the discussion herein. Further,while the figures illustrate the functional components and data of theimage display apparatus 700 as being present on the image displayapparatus 700 and executed by the processor 702 on the image displayapparatus 700, it is to be appreciated that these components and/or datamay be distributed across different computing devices and locations inany manner.

FIG. 7 further illustrates examples of other components that may beincluded in the image display apparatus 700. Such examples includevarious types of sensors, which may include a GPS device 712, anaccelerometer 714, one or more cameras 716, a compass 718, a gyroscope720, a microphone 722, and so forth.

The image display apparatus 700 may further include one or morecommunication interfaces 724, which may support both wired and wirelessconnection to various networks, such as cellular networks, radio, Wi-Finetworks, close-range wireless connections, near-field connections,infrared signals, local area networks, wide area networks, the Internet,and so forth. The communication interfaces 724 may further allow a userto access storage on or through another device, such as a remotecomputing device, a network attached storage device, cloud storage, orthe like.

The image display apparatus 700 may further be equipped with one or morespeakers 726 and various other input/output (I/O) components 728. SuchI/O components 728 may include a touchscreen and various user controls(e.g., buttons, a joystick, a keyboard, a keypad, etc.), a haptic ortactile output device, connection ports, physical condition sensors, andso forth. For example, the operating system 706 of the image displayapparatus 700 may include suitable drivers configured to accept inputfrom a keypad, keyboard, or other user controls and devices included asthe I/O components 728. Additionally, the image display apparatus 400may include various other components that are not illustrated, examplesof which include removable storage, a power source, such as a batteryand power control unit, a PC Card component, and so forth.

Various instructions, methods and techniques described herein may beconsidered in the general context of computer-executable instructions,such as program modules stored on computer storage media and executed bythe processors herein. Generally, program modules include routines,programs, objects, components, data structures, etc., for performingparticular tasks or implementing particular abstract data types. Theseprogram modules, and the like, may be executed as native code or may bedownloaded and executed, such as in a virtual machine or otherjust-in-time compilation execution environment. Typically, thefunctionality of the program modules may be combined or distributed asdesired in various implementations. An implementation of these modulesand techniques may be stored on computer storage media or transmittedacross some form of communication.

Although the subject matter has been described in language specific tostructural features and/or methodological acts, it is to be understoodthat the subject matter defined in the appended claims is notnecessarily limited to the specific features or acts described. Rather,the specific features and acts are disclosed as illustrative forms ofimplementing the claims.

One skilled in the art will realize that a virtually unlimited number ofvariations to the above descriptions are possible, and that the examplesand the accompanying figures are merely to illustrate one or moreexamples of implementations.

It will be understood by those skilled in the art that various othermodifications can be made, and equivalents can be substituted, withoutdeparting from claimed subject matter. Additionally, many modificationscan be made to adapt a particular situation to the teachings of claimedsubject matter without departing from the central concept describedherein. Therefore, it is intended that claimed subject matter not belimited to the particular embodiments disclosed, but that such claimedsubject matter can also include all embodiments falling within the scopeof the appended claims, and equivalents thereof.

In the detailed description above, numerous specific details are setforth to provide a thorough understanding of claimed subject matter.However, it will be understood by those skilled in the art that claimedsubject matter can be practiced without these specific details. In otherinstances, methods, devices, or systems that would be known by one ofordinary skill have not been described in detail so as not to obscureclaimed subject matter.

Reference throughout this specification to “one embodiment” or “anembodiment” can mean that a particular feature, structure, orcharacteristic described in connection with a particular embodiment canbe included in at least one embodiment of claimed subject matter. Thus,appearances of the phrase “in one embodiment” or “an embodiment” invarious places throughout this specification are not necessarilyintended to refer to the same embodiment or to any one particularembodiment described. Furthermore, it is to be understood thatparticular features, structures, or characteristics described can becombined in various ways in one or more embodiments. In general, ofcourse, these and other issues can vary with the particular context ofusage. Therefore, the particular context of the description or the usageof these terms can provide helpful guidance regarding inferences to bedrawn for that context.

What is claimed is:
 1. A method of sealing an electrowetting device,wherein the electrowetting device comprises a first fluid and a secondfluid disposed between a first substrate and a second substrate, thefirst fluid being immiscible with the second fluid, the methodcomprising: providing the first substrate; providing the secondsubstrate; applying an adhesive/sealing material on at least a portionof the first substrate or at least a portion of the second substrate,wherein the adhesive/sealing material includes particles that alterrheological properties of the adhesive/sealing material; and couplingthe first substrate to the second substrate via the adhesive/sealingmaterial such that the adhesive/sealing material is in contact with thesecond fluid.
 2. The method of claim 1, wherein the adhesive/sealingmaterial includes particles comprising one or more of (i) clay particlesin a range of 0-5% mass fraction of clay particles or (ii) ceramicparticles in a range of 0-5% mass fraction of ceramic particles.
 3. Themethod of claim 2, wherein the adhesive/sealing material includes one ormore of (i) clay particles having a size in a range of 6-39 nanometersor (ii) ceramic particles having a size in a range of 6-39 nanometers.4. The method of claim 1, wherein the adhesive/sealing material includessilica particles.
 5. The method of claim 4, wherein the silica particlesare hydrophobic silica particles.
 6. The method of claim 4, wherein thesilica particles are hydrophilic silica particles.
 7. The method ofclaim 4, wherein the silica particles have a size in a range of 6-39nanometers.
 8. The method of claim 1, wherein the adhesive/sealingmaterial includes silica particles in a range of 0-5% mass fractionsilica.
 9. A method of sealing first and second substrates of a displaydevice that includes a fluid between the first and second substrates,the method comprising: applying an adhesive/sealing material on at leasta portion of the first substrate or at least a portion of the secondsubstrate such that the adhesive/sealing material is in contact with thefluid, wherein the adhesive/sealing material includes particlesaffecting rheological properties of the adhesive/sealing material; andjoining the first substrate with the second substrate via theadhesive/sealing material.
 10. The method of claim 9, wherein applyingthe adhesive/sealing material further comprises applying theadhesive/sealing material in a pre-determined pattern onto the firstsubstrate or the second substrate.
 11. The method of claim 9, wherein avolume between the first substrate and the second substrate defines adisplay region, and wherein applying the adhesive/sealing materialfurther comprises applying the adhesive/sealing material initiallyoutside the display region and subsequently applying theadhesive/sealing material in a pre-determined pattern onto the firstsubstrate or the second substrate within the display region.
 12. Themethod of claim 9, wherein applying the adhesive/sealing materialfurther comprises applying the adhesive/sealing material directly on atransparent conductive layer disposed on the first substrate or thesecond substrate.
 13. The method of claim 9, wherein theadhesive/sealing material includes one or more of (i) clay particleshaving a size in a range of 6-39 nanometers or (ii) ceramic particleshaving a size in a range of 6-39 nanometers.
 14. A method comprising:combining an adhesive/sealing material with particles that affectrheological properties of the adhesive/sealing material to produce amodified adhesive/sealing material; applying the modifiedadhesive/sealing material onto at least a portion of a first substrateof a display device or at least a portion of a second substrate of thedisplay device such that the modified adhesive/sealing material is incontact with a fluid disposed on the first substrate or the secondsubstrate; and joining the first substrate with the second substrate viathe modified adhesive/sealing material.
 15. The method of claim 14,wherein the adhesive/sealing material includes silica particles.
 16. Themethod of claim 14, wherein the modified adhesive/sealing material has aparticular yield stress, and wherein applying the modifiedadhesive/sealing material further comprises dispensing the modifiedadhesive/sealing material with a dispensing force that is greater thanthe yield stress.
 17. The method of claim 16, wherein combining theadhesive/sealing material with particles that affect the rheologicalproperties of the adhesive/sealing material further comprises:increasing an amount of the particles that are combined with theadhesive/sealing material at least until the modified adhesive/sealingmaterial has the particular yield stress.
 18. The method of claim 14,wherein the adhesive/sealing material includes silica particles in arange of 0-5% mass fraction silica.
 19. The method of claim 14, whereinapplying the modified adhesive/sealing material further comprisesapplying the modified adhesive/sealing material directly on atransparent conductive layer disposed on the first substrate or thesecond substrate.
 20. The method of claim 14, wherein the modifiedadhesive/sealing material includes particles comprising one or more of(i) clay particles in a range of 0-5% mass fraction of clay particles or(ii) ceramic particles in a range of 0-5% mass fraction of ceramicparticles.